This rickettsial disease is transmitted via lice and probably ticks. The infective agent is Bartonella (Rochalimaea) quintana.
In one US study, DNA of Bartonella organisms was found in nearly 20% of ticks.
Trench fever was a significant medical problem during World War I; troops caught it on the battlefield and lice spread the disease. It has recently reappeared among AIDS victims and homeless and alcoholic persons. Here lice are not a factor and ticks are suspected.